Rotation
Day/night from Earth's rotation (~24 h).
Rotation
Earth's Rotation
What you'll learn
- Rotation — Earth spinning on its axis once in about 24 hours.
- How rotation causes day and night — the side facing the Sun has daylight.
- Direction of spin and why the Sun appears to move across the sky.
- To link with NCERT Looking Around 5, Chapter 11 (Sunita in Space) — 16 sunrises in 24 hours on ISS (fast orbit).
Key concepts
Level 1 — Day and night
Verbal: Earth rotates from west to east; each full turn ≈ 24 hours.
Symbolic: 1 rotation ≈ 24 h → one day-night cycle.
| Side of Earth | Facing Sun? | Experience |
|---|---|---|
| Day side | Yes | Daylight, warmer |
| Night side | No | Dark, stars visible (if clear) |
| Terminator | Boundary | Sunrise or sunset |
NCERT link: Ch 11 contrasts Earth's rotation with ISS orbiting Earth every ~90 minutes.
Level 2 — Apparent motion of Sun
Verbal: Sun seems to rise in the east and set in the west because we rotate toward the east.
Real-life: At noon, Sun is roughly south in India (northern hemisphere) — shadow shortest.
| Event | Cause |
|---|---|
| Sunrise | Your location rotates into sunlight |
| Sunset | Your location rotates out of sunlight |
| Stars at night | Same rotation — different sky view |
Worked example
Why is it day in India when it is night in Brazil?
Step 1 — Earth is sphere; Sun lights half at a time.
Step 2 — India and Brazil on opposite sides → opposite lighting.
Answer: Different sides of Earth face the Sun.
ISS sees many sunrises per day. Why?
Step 1 — ISS orbits Earth fast (~90 min), not just rotating with surface.
Step 2 — Enters sunlight and shadow repeatedly.
Answer: Fast orbit around Earth, separate from Earth's 24 h rotation.
Common mistakes
| Mistake | Why it happens | Fix |
|---|---|---|
| Sun moves around Earth daily | Appearance vs reality | Earth rotates; Sun appears to move |
| Day/night from Earth orbiting Sun | Mixing rotation and revolution | Rotation → day/night; revolution → year |
| 12 h day everywhere always | Ignoring seasons/t latitude | Day length varies by season and location |
| Rotation and revolution same | Similar words | Rotation = spin; revolution = orbit around Sun |
Quick check
- How long is one rotation of Earth (approx.)?
- What causes day and night?
- In which direction does Earth rotate (west to east)?
- Stretch: If Earth stopped rotating, what would happen to day and night?
Revision tip: Draw a circle (Earth) and a lamp (Sun). Rotate the circle slowly — mark where your city has day vs night.
Open the Practice tab for graded questions on Earth's Rotation.
Key Takeaways (TL;DR)
- What you'll learn
- Key concepts
- Worked example
- Common mistakes
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